Halogen containing polymers tend to degrade or deteriorate when processed. Generally, the difference between the processing temperature and the degradation temperature is very small. Therefore, there is a risk that during the processing of these halogen containing polymers, that the polymer will degrade. When such polymers degrade, it is believed that the halide acid generated by the polymer attacks the components of the processing equipment. Also, this acid further catalyzes elimination reactions and additional degradation of the polymer.
Stabilizers have been developed to help deter such degradation. For example, organic compounds are commonly used. In some instances, zeolites have also been used as stabilizers.
Zeolites are effective acid scavengers for halogen containing polymers and enhance the thermal stability of halogen containing polymers. Acid scavengers are compounds that react with acids to form a compound that is typically chemically inert. However, the use of zeolites as stabilizers or acid scavengers in halogen containing polymer compounds has been limited for several reasons. First, the zeolites generally have a large particle size, generally in the range of about 3 to about 6 microns. The large size of the zeolite particles not only causes surface blemishes on the finish of the end product made from such a polymer but also diminishes the physical properties of such polymers. Further, outgassing occurs frequently with polymers containing zeolites when the polymer is heated during processing due to the evolution of water from the zeolite during the heating. As a result, there is foaming.
U.S. Pat. No. 4,000,100 discloses a thermal and light stabilized polyvinyl chloride resin. The stabilizer used in the composition comprises an unactivated zeolite A molecular sieve or an unactivated naturally occurring molecular sieve of essentially the same pore size range as zeolite A and a conventional inorganic, organometallic or organic stabilizer. The unactivated zeolite molecular sieve has adsorbed water molecules. According to the patentee, the combination of the unactivated zeolite and the conventional stabilizer produces a compound with allegedly improved stability as compared to a compounds produced with either of the two stabilizers separately.
Similarly, U.S. Pat. No. 4,338,226 discloses a process for the stabilization of polyvinyl chloride and stabilizer compositions. The patent describes admixing sodium aluminosilicate of small particle size (preferably, 0.1 to 20 microns), calcium salts of fatty acids, zinc salts of fatty acids, partial esters of polyols and fatty acids, thioglycolic acid esters of polyols and polyvinyl chloride or copolymer of vinyl chloride. An aluminosilicate that can be used is crystalline sodium zeolite A. The composition is used for molding mixtures.
U.S. Pat. No. 4,371,656 describes a metal substituted zeolite for use as a stabilizer for halogen containing resins. The stabilizer comprises a crystalline aluminosilicate substituted with ions of metallic elements belonging to Group II or Group IVA of the Periodic Table for the Group I (M) metal ion contained in the aluminosilicate. The stabilizer also must contain 10% by weight or less as M.sub.2 O of residual Group I metal ions. The stabilizer, zeolite A, according to the patentee claims to have a water content of 8% by weight or less. This patent also discloses the use of organic substances to cover the voids of the zeolite particles and prevent moisture reabsorption.
Stabilized chloride containing resins are also described in U.S. Pat. No. 5,004,776. The stabilizer consists essentially of: (a) an overbased alkaline earth metal carboxylate or phenolate complex; (b) zeolite; (c) calcium hydroxide; and (d) a complex of at least one metal perchlorate selected from the group consisting of sodium, magnesium, calcium, and barium perchlorates with at least one compound selected from the group consisting of polyhydric alcohols and their derivatives. This stabilizer apparently prevents the discoloration and deterioration in physical properties of the chlorine containing resin resulting from thermal degradation when the resin is subject to thermoforming or exposed to a high temperature atmosphere for a long period of time.
Stabilizer compositions for use in halogen containing polymer are also described in U.S. Pat. No. 5,216,058. The stabilizer composition comprises hydrotalcite and a molecular sieve zeolite. The molecular sieve zeolite comprises a Group IA or IIA aluminosilicate.
U.S. Pat. No. 5,582,873 discloses an acid scavenger stabilized halogen containing organic polymer. The patent also describes the method for processing such a polymer. The composition comprises a halogen containing polymer, an zeolite as the acid scavenger and a heat stabilizer selected from the group consisting of mixed metal stabilizers, organtotin stabilizers, lead stabilizers, metal free stabilizers or any combination thereof. The acid scavengers are sodium zeolites which have a 13 to 25% water content, and a mean particle size of about 3 to about 5 microns.
Thus, there currently exists a need for a halogen containing polymer compound having improved process stability. In particular, a need exists for a stabilizer for a halogen containing compound comprising a modified zeolite which maintains the physical properties of the halogen containing polymer. More particularly, a need exists for a modified zeolite stabilizer for use in chlorinated polyvinyl chloride and polyvinyl chloride compounds. More particularly, there exists a need for a chlorinated polyvinyl chloride compound which has improved processability including excellent heat stability.